Lotus Elan

CV drive shaft conversion

PostPost by: 2cams70 » Sun Jan 28, 2024 3:34 pm

Certainly seems to be quite a few nuts with lots of dough on this forum
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PostPost by: alanr » Sun Jan 28, 2024 3:49 pm

2cams70 wrote:Certainly seems to be quite a few nuts with lots of dough on this forum


Very good!. Made me laugh! :lol

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PostPost by: draenog » Sun Jan 28, 2024 4:01 pm

I am an originality nut, keeping everything as original as possible. This included keeping rotoflexes (they were replaced just before I collected the car). But you do not want a rotoflex failure, and I wish I had replaced them earlier.

I checked them regularly, every couple of months, and there was no sign of deterioration. But in September 2021 I took the car out for one of my usual (reasonably spirited) drives. Turning off from one road to another, there was a fairly steep hill. Putting my foot down, there was an almighty bang and then lots of banging and thudding. After a couple of seconds I realised what must have happened, but stopping on a single lane country road halfway up a steep hill was not ideal! When I went to put the handbrake on, it didn't work (it was wrapped around the driveshaft). Even with the car in gear it was rolling backwards (cue lots of frantic emptying of the boot of spare wheel, jack and anything else to jam under the wheels).

In the end, I think I was fairly lucky damage-wise. The handbrake rods/tree had to be completely replaced (and calipers stripped down to bend the operating levers back). The chassis took a lot of pounding, which had to be straightened out and welded. The wishbone was also completely destroyed. Fibre-glass damage was limited to a couple of impact areas where the brake caliper hit (the wheel was pushed backwards).

I'd overhauled the front suspension during 2019/2020, so the back was next inline, anyway. So it no longer looks like the grotty photos. But it was off the road for another 8 months, just when I wanted to drive it after lockdown :(

I still don't know why the rotoflex failed. The rubber had split along one of the strengthening metal inserts, but I'm not sure if that was the failure or it happened as a result. You may be able to see from the photo that all the bolts holding the rotoflex to the differential output shaft are missing. I went along the road trying to find them (I had plenty of time in the 8 hours it took to be recovered).

I found one bolt shaft and one nut-end, which were obviously from different bolts. Perhaps the bolts had come loose, and the stress had caused them to break? This is not something that can be checked from visual inspection. So another reason to replace the rotoflexes. They're simply not worth the fuss of a failure.

rotoflex-chassis-damage.jpg and

rotoflex-failure.jpg and

rotoflex-failure2.jpg and

rotoflex-grp-damage.jpg and
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PostPost by: rgh0 » Sun Jan 28, 2024 4:10 pm

The drive shaft bolts will fatigue and break if not tightened adequately(or come loose) or not a good quality grade 5 bolt. This is more likely in a Donut set up compared to Cvs where the bolt is subject to more complex and higher bending loads by the donut and the resulting failure of just 1 bolt leaves a lot of damage. In a Cv has one loose bolt is less likely to cause catastrophic damage.

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PostPost by: Breezehill » Sun Jan 28, 2024 6:38 pm

All, thanks so far for all the honest opinions.

For all and Allan, the car a late 1970 +2S appeared in Club Lotus magazine about three years ago after we’d just bought it back and known as The Prodical Lotus. Correct bought back having first bought the car as a project back in the late 70’s when it was in a state, unloved, badly maintaind along with damaged chassis where some numpty had jacked the car on the front cross member which was badly punctured allowing the section and drivers side upright to rot.

So new Spyder chassis a full nut and bolt rebuild, all bolts assembled using copper grease. And most of the running gear where necessary replaced. The whole scenario took five years, two house moves before returning to the road in the early 80’s. However and I’m sure there are some out here who experienced the same when children arrived somewhat to go sadly the Lotus. Once sold did keep in touch with the new owner who shared the various car events where he’d won best in class, really did cheer me up.

Moving on 2019, just scanning the pages of the usual online car magazines and always checking the Lotus for sale spotted one that looked very similar then zoomed in on the picture and bingo it was our old Lotus. Contacted the dealer just for a chat and sent some photos of the rebuild I’d done. Basically suggested that the new owner could contact me and I’d run them through all the work that had been done. On a whim decided to go and see the car, guess what bought it.

Sadly the car had been standing outside unloved for a couple of years, mice had taken up residence in the boot and behind the panels where the seat belts are fitted along with damp in the carpets which needed ripping out.

So car back with us, all trim taken out and mice nests removed we put it back together to get it back on the road for summer. Oh yes, the mice had eaten through the loom in the boot and behind the seat belt panels so new harness throughout.

We’ve now used the car and trips around our area to local car meets and the pub. However our last trip out last autumn there was a grinding noise from the rear which showed as failed bearings in the drivers side rear. Since then the car has been up in the air in our workshop, where the rear running gear, diff and suspension has been removed hence why I now have the question on CV drive shafts. Thank goodness for the initial rebuilding using copper grease on all bolts meant they all came apart.

We don’t do great distance with the car and mainly only during the best days of summer etc. mileage wise probably most 5000 per annum.

So does it warrant CV or retain doughnuts ?
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PostPost by: alanr » Sun Jan 28, 2024 7:19 pm

Well I think you have answered your own question really.
You have previously owned the car,really know the car and all it's foibles, done lots of miles in it, know how it drives on doughnuts, and have previously been happy on rotoflex doughnuts. So therefore if I were you I would keep your money in your pocket and retain the doughnuts!
No brainer to my way of thinking!

Alan...(Note:- One 'L' only, thank you.)
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PostPost by: JonB » Sun Jan 28, 2024 9:10 pm

CVs is my advice. Fit and forget. As others have said, you can get a sudden catastrophic fail with a Rotoflex joint despite regularly checking it. Take no chances with your safety, especially in a fibreglass car that has zero side impact protection.

Yours looks like a 130/5 which will have the diff brace as standard. So was mine, I fitted CVs and drove spiritedly. I didn't put new frustacones in (the diff flexible top mount) and I didn't have any problems. The originality thing is out of the window anyway because you have a Spyder chassis.
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PostPost by: Foxie » Mon Jan 29, 2024 12:41 am

I've posted on the subject of donuts v. cvjs a number of times since I converted my +2S over 20 years ago, but I'll post again here for the benefit of the present topic.

I've had the car now for 39 years, and have raced and hillclimbed it for the last 16 years. The present 1860 engine has been dyno'd at 169 bhp

Donuts never lasted very long, 20k miles at best before starting to crack and come apart. The last catastrophic failure (in heavy traffic ) broke off the complete brake caliper from the suspension leg casting. No drive, no brakes, no handbrake, and a very red face !

I fitted CVJs supplied by Spyder. That was over 20 years ago, and they're still perfect.

Imho the "drive cushion design" is a salesman's turnaround put out by a clever ACBC to hide the real reason for the donuts. They were cheap.

:)
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PostPost by: Baggy2 » Mon Jan 29, 2024 2:25 am

[quote]Imho the "drive cushion design" is a salesman's turnaround put out by a clever ACBC to hide the real reason for the donuts. They were cheap.[/quote ]

Nowadays a CV joint conversion isn't that much more expensive than 4 x donuts. Given that the donuts have a much shorter life the CV joint seems to be the obvious way to go - Its the way I went last time I was faced with the choice.

One thing I don't think Colin would have liked is the increased unsprung weight but I guess there are always trade offs.

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PostPost by: 2cams70 » Mon Jan 29, 2024 2:38 am

I don’t think it’s fair to say that doughnuts were fitted just because they were cheap. They were the best things available to do the job at the time. Universal joints as were commonly available at the time had their disadvantages - they are called universal joints and not constant velocity joints for a good reason. UJ’s were probably OK for the race track at that time but not so good for long term on road use. I know jags had UJ’s but the track width is much longer on a jag compared to a Lotus.

If the car had been designed to use CV’s from the outset perhaps other changes might have been considered as well - eg strengthening the diff housing mounting ears but who knows? These days if it works it works if it doesn’t work it doesn’t work.
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PostPost by: StressCraxx » Mon Jan 29, 2024 3:19 am

2cams70 wrote:I don’t think it’s fair to say that doughnuts were fitted just because they were cheap. They were the best things available to do the job at the time. Universal joints as were commonly available at the time had their disadvantages - they are called universal joints and not constant velocity joints for a good reason. UJ’s were probably OK for the race track at that time but not so good for long term on road use. I know jags had UJ’s but the track width is much longer on a jag compared to a Lotus.

If the car had been designed to use CV’s from the outset perhaps other changes might have been considered as well - eg strengthening the diff housing mounting ears but who knows? These days if it works it works if it doesn’t work it doesn’t work.


Exactly. Chapman and his team were well aware of u-joint and sliding splines limitations. If u-joints were used the rear struts could not have allowed nearly as much bump or droop travel.

Chapman used U-joints combined with rubber donuts, without sliding splines on the Lotus 23 in 1962. The 23 had less suspension travel than the Elan.

The Datsun 510 (Nissan Bluebird for the rest of the world) used sliding spline u-joints on a semi-trailing arm rear suspension. Only about 5" of total suspension travel and one was lucky to have a set last 35-40,000 miles.
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PostPost by: mjbeanie » Mon Jan 29, 2024 5:10 am

This was a great thread with some very helpful information! I am working through this same rear drive dilemma. My car can now move under power for the first time, after two years of restoration. The rotoflex are toast and I will not be driving it except for some brief tests in front of my home. I've spent hours reviewing almost every supplier. In the end, I chose Elantrikbits, down under, to make up my CV conversion kit. (Sue Miller was a close second and somewhat less expensive) However, I was impressed with the offerings from Elantrikbits. Their machine shop capabilities, overall quality, product design, and customer service appear excellent. My kit has been ordered, and is being manufactured as we speak.

Once received, I'll post some picts of the kit as unboxed, and add some technical details as I install it on my 71 Plus 2, -currently with some very tired looking donuts, see photo. I am looking forward to the installation and a smoother acceleration.
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PostPost by: 2cams70 » Mon Jan 29, 2024 7:19 am

That explains a lot of things that you guys have been going to the cake shop to get doughnuts for your car. I hope you haven’t been eating the leftovers of the doughnuts your car previously had fitted.

To all you pussycats complaining about the dangers of driving cars fitted with doughnuts living on the edge is all part of the authentic Lotus experience so stop whingeing.

If you think that’s bad then try driving one of those things with the engine in the wrong position at the limit (the make of which I can never remember). Then you’d really have something to complain about.
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PostPost by: englishmaninwales » Mon Jan 29, 2024 9:52 am

2cams70 wrote:…To all you pussycats complaining about the dangers of driving cars fitted with doughnuts living on the edge is all part of the authentic Lotus experience so stop whingeing…


I’ve just re-read the thread. Certainly some strong, helpful views for and against CV/ rotorflex couplings have been expressed, but I can’t say there has been any whingeing, as you describe.

But I suppose that is just a matter of opinion.
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PostPost by: 661 » Mon Jan 29, 2024 10:31 am

After a catastrophic failure of the doughnuts in the S4 about 30 years ago I fitted Spyder CVs with the retention of one of the doughnuts. A half hearted solution ( doughnut still require all the usual maintenance and changing)and have since replaced for Col's Elantrikbits CV. A marvel of engineering.
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